title: Modification of keap1 cysteine residues by sulforaphane.
abstract: Activation of the transcription factor NF-E2-related factor-2 (Nrf2) through modification of Kelch-like ECH-associated protein 1 (Keap1) cysteines, leading to up-regulation of the antioxidant response element (ARE), is an important mechanism of cellular defense against reactive oxygen species and xenobiotic electrophiles. Sulforaphane, occurring in cruciferous vegetables such as broccoli, is a potent natural ARE activator that functions by modifying Keap1 cysteine residues, but there are conflicting in vitro and in vivo data regarding which of these cysteine residues react. Although most biological data indicate that modification of C151 is essential for sulforaphane action, some recent studies using mass spectrometry have failed to identify C151 as a site of Keap1 sulforaphane reaction. We have reconciled these conflicting data using mass spectrometry with a revised sample preparation protocol and confirmed that C151 is indeed among the most readily modified cysteines of Keap1 by sulforaphane. Previous mass spectrometry-based studies used iodoacetamide during sample preparation to derivatize free cysteine sulfhydryl groups causing the loss of sulforaphane from highly reactive and reversible cysteine residues on Keap1 including C151. By omitting iodoacetamide from the protocol and reducing sample preparation time, our mass spectrometry-based studies now confirm previous cell-based studies which showed that sulforaphane reacts with at least four cysteine residues of Keap1 including C151.
authors.affiliation: Department of Medicinal Chemistry and Pharmacognosy, University of Illinois College of Pharmacy, 833 S. Wood Street, Chicago, IL 60612, United States.
authors.forename: Chenqi
authors.initials: C
authors.lastname: Hu
authors.forename: Aimee L
authors.initials: AL
authors.lastname: Eggler
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Mesecar
authors.forename: Richard B
authors.initials: RB
authors.lastname: van Breemen
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000737:chemistry*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017879:Isothiocyanates; D000072019:Kelch-Like ECH-Associated Protein 1; D010455:Peptides / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020218:Response Elements; D013454:Sulfoxides; D053719:Tandem Mass Spectrometry; D013861:Thiocyanates / Q000737:chemistry*; D015854:Up-Regulation
chemical_list: D000975:Antioxidants; D047908:Intracellular Signaling Peptides and Proteins; D017879:Isothiocyanates; C431364:KEAP1 protein, human; D000072019:Kelch-Like ECH-Associated Protein 1; D010455:Peptides; D011994:Recombinant Proteins; D013454:Sulfoxides; D013861:Thiocyanates; C016766:sulforaphane; D003545:Cysteine